Electrically conductive textile element and method of producing same

ABSTRACT

A method of producing an electrically conductive textile element that includes the steps of modifying a surface of a textile element with a negatively-charged polyelectrolyte; and coating the modified surface of the textile element with metal particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/554,695, filed Aug. 30, 2017, which is incorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates to the field of electrically conductive textile elements and methods of producing same.

BACKGROUND OF THE INVENTION

With the rapid advancement of flexible and wearable electronic devices there has been a demand for conductors as interconnects, contacts, electrodes and metal wires which can be integrated into conductive textiles/garments. Accordingly, methods for synthesizing fabricated high performance electrically conductive textiles have been developed including synthesizing of yarns by or incorporated with metal wires, metal oxide, intrinsically conducting polymers (ICPs), and carbon nanotubes (CNTs). However, conductive textiles fabricated in accordance with these existing methods are not ideal due to their inflexibility, chemical instability, cost of production, hazards posed to the human body, and most significantly, the difficulties associated with large scale production with compatible technology in the current textile and garment industry.

Another approach to synthesizing conductive textiles involves depositing metal coatings on to textile substrate surfaces utilising various metal particle deposition techniques. However, there are also limitations associated with this approach in terms of the relative amount of investment in technology, advanced instrumentation and specialized workforce expertise involved, as well the relatively precise control parameters required which limit industrialization of this process commercially. Furthermore, adhesion of the deposited metal on the textile surface remains another major concern on the durability and conductivity of such conductive textiles.

Further processes have been developed which involve modifying the surface architecture of textile substrates by grafting of functionalized polymer brushes thereon. In particular, polyelectrolytes that covalently tether one end on a textile substrate surface may not only provide modified functional groups on the textile substrate surface, but also increase the amount of functional groups to be utilized in subsequent chemical reactions. By way of example, Azzaroni et al., demonstrated the grating of positively-charged poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PMETAC) polyelectrolytes on to a substrate surface. With the loading of catalytic moieties tetrachloropalladtae(II) anion ([PdCl4]2−) for subsequent metal electroless deposition (ELD), a robust metal layer is able to be selectively deposited with suitable adhesion properties. In 2010, Liu et al. reported a versatile approach to prepare durable conductive cotton yarns also by growing PMETAC brushes on cotton fiber surfaces using surface-initiated atom transfer radical polymerization (SI-ATRP), which was the first ever demonstration on grafting of PMETAC brushes on natural textile fibers. Subsequent metal ELD yielded conductive cotton yarns with high electrical stability that is able to withstand multiple bending, stretching, rubbing and even washing cycles. However, the feasibility of scale production of the SI-ATRP method taught by Liu et al. suffers from various problems. For instance, SI-ATRP is not able to be suitable performed under ambient conditions and requires nitrogen protection. Furthermore, the SI-ATRP reaction involves a relatively long period of time (˜24 hours) which is undesirable and not cost-effective for mass production. Thus, there is a need to modify the synthesizing process to allow for high throughput conductive textile production.

Other attempts have been made to modify the synthesizing approach by preparing electrically conductive fibers, yarns and fabrics by deposition of metals onto various textile substrates which are prior-modified with the same positively-charged polyelectrolytes PMETAC using in-situ free radical polymerization. In-situ free radical polymerization may increase the throughput of the polymerization of polyelectrolytes. Generally, the reaction only takes up ˜1-3 hours to complete and can be carried out under ambient conditions, which is highly advantageous over other polymerization methods such as previously mentioned SI-ATRP. However, this modified approach suffers from a drawback in that as the selection of catalytic moieties highly depends on the properties and nature of polyelectrolyte brush that grafted on the textile surface, cationic PMETAC is restricted to couple with anionic [PdCl4]2− moieties for subsequent electroless metal deposition. Furthermore, the [PdCl4]2− moieties used are relatively expensive (USD159.5 per 2 grams for 97% ammonium tetrachloropalladate(II)). Even though the anionic [PdCl4]2− moieties can be reused, it is still not economical if it is used in the mass production.

SUMMARY OF THE INVENTION

The present invention seeks to alleviate at least one of the above-described problems.

The present invention may involve several broad forms. Embodiments of the present invention may include one or any combination of the different broad forms herein described.

In a first broad form, the present invention provides a method of producing an electrically conductive textile element including the steps of:

(i) modifying a surface of a textile element with a negatively-charged polyelectrolyte; and

(ii) coating the modified surface of the textile element with metal particles.

Preferably, the step (i) may include modifying the surface of the textile element with a negatively-charged polyelectrolyte by in-situ free radical polymerisation.

Preferably, the negatively-charged polyelectrolyte may includes at least one of poly(methacrylic acid sodium salt) and poly(acrylic acid sodium salt).

Preferably, the step (i) may include modifying a silanized surface of a textile element with a negatively-charged polyelectrolyte.

Preferably, the step (ii) may include coating the modified surface of the textile element with metal particles by electroless metal deposition.

Preferably, the metal particles may include at least one of copper and nickel particles.

Preferably, the textile element may include at least one of a yarn and a fiber configured for being formed in to a fabric.

Preferably, the textile element may include at least one of a polyester, nylon, cotton and silk yarn or fiber.

In a further broad form, the present invention provides an apparatus for producing an electrically conductive textile element including:

an apparatus for modifying a surface of a textile element with a negatively-charged polyelectrolyte; and

a coating apparatus for coating the modified surface of the textile element with metal particles.

Preferably, the apparatus for modifying the surface of the textile element with the negatively-charged polyelectrolyte may be configured to modify the surface of the textile element with a negatively-charged polyelectrolyte by in-situ free radical polymerisation.

Preferably, the negatively-charged polyelectrolyte may include at least one of poly(methacrylic acid sodium salt) and poly(acrylic acid sodium salt).

Preferably, the apparatus for modifying the surface of the textile element with the negatively-charged polyelectrolyte may be configured to modify a silanized surface of a textile element with a negatively-charged polyelectrolyte.

Preferably, the coating apparatus may be configured to coat the modified surface of the textile element with metal particles by electroless metal deposition.

Preferably, the metal particles may include at least one of copper and nickel particles.

Preferably, the textile element may include at least one of a yarn and a fiber configured for being formed in to a fabric.

Preferably, the textile element may include at least one of a polyester, nylon, cotton and silk yarn or fiber.

In a further broad form, the present invention provides an electrically conductive textile element produced in accordance with the method steps of the first broad form of the present invention.

In a further broad form, the present invention provides a fabric formed from at least one textile element wherein the at least one textile element is produced in accordance with the method steps of the first broad form of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the following detailed description of a preferred but non-limiting embodiment thereof, described in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a process of preparing conductive cotton yarns via in-situ free radical polymerization in accordance with an embodiment of the present invention;

FIG. 2 depicts an exemplary copper-coated cotton yarn fabricated in accordance with the method depicted in FIG. 1;

FIG. 3 depicts a representation of Fourier transform infrared spectroscopy (FTIR) spectra data in respect of pristine cotton yarns, silane-modified cotton, and PMANa-modified cotton yarns formed in accordance with an embodiment of the present invention;

FIG. 4 depicts a representation of EDX spectrum of PMANa-modified cotton produced in accordance with an embodiment of the present invention;

FIG. 5 depicts SEM images representing surface morphologies of cotton fibers with different modifications including (A) pristine cotton; (B) silane-modified cotton; (C) PMANa-coated cotton; (D-F) copper-coated cotton in accordance with an embodiment of the present invention;

FIG. 6 depicts data representing (A) linear resistance of the as-synthesized copper-coated cotton yarns and (B) Tensile strength of the cotton yarns produced in accordance with an embodiment of the present invention;

FIG. 7 depicts process steps for fabrication of a woven fabric formed from copper-coated yarns produced in accordance with an embodiment of the present invention;

FIG. 8 depicts sheet resistance data of fabrics woven from copper-coated yarns produced in accordance with an embodiment of the present invention;

FIG. 9 depicts SEM images of cotton yarns unraveled from washed fabrics under different washing times, the cotton yarns being produced in accordance with an embodiment of the present invention;

FIG. 10 depicts a PMANa-assisted nickel-coated cotton fabric produced in accordance with an embodiment of the present invention;

FIG. 11A depicts an exemplary PAANa-assisted copper-coated yarn formed in accordance with an embodiment of the present invention;

FIG. 11B depicts an exemplary PAANa-assisted nickel-coated silk yarn formed in accordance with an embodiment of the present invention;

FIG. 12A depicts PAANa-assisted copper-coated nylon yarn produced in accordance with an embodiment of the present invention; and

FIG. 12B depicts a polyester fabric formed from PAANa-assisted copper-coated nylon yarn produced in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will now be described with referenced to the FIGS. 1 to 12B.

Referring firstly to FIG. 1, a procedure for preparing PMANa polyelectrolytes on textile substrates such as cotton yarn is illustrated schematically. The embodiment involves an in-situ free radical polymerization method which may be performed upon cotton yarns by way of example to prepare poly(methacrylic acid sodium salt) (PMANa)-coated cotton yarns. Subsequent ion exchange, ion reduction and electroless deposition of metal particles onto the PMANa-coated cotton yarns may then be performed in order to yield electrically conductive cotton yarns of suitable quality for production on a commercial scale. It should be noted that this embodiment may also be applicable to the preparation of PAANa polyelectrolytes on textile substrates.

In performing the process, cotton yarns are first immersed in a solution of 5-20% (v/v) C═C bond bearing silane for approximately 30 minutes so as to allow the hydroxyl groups of cellulose to suitably react with the silane molecules. The cotton yarns are then rinsed thoroughly with fresh deionized (DI) water so as to remove any excess physical adsorbed silane and by-product molecules. This step of silanisation is represented by (100) in FIG. 1.

The rinsed cotton yarns are then placed into an oven at 100-120° C. for between approximately 15-30 minutes to complete the condensation reaction. Subsequently, the silane-modified cotton yarns are immersed into approximately 50 mL aqueous solution comprising of 3-7 g of MANa powder and 35-75 mg of K2S2O8 (similarly, AANa powder may be used in respect of PAANa polyelectrolytes). The whole solution mixture with cotton yarns is heated at 60-80° C. in an oven for 0.5-1 hour in order to carry out the free radical polymerization. In the free radical polymerization process, the double bond of silane can be opened by the free radicals resulting in the growth of PMANa polyelectrolyte onto the cotton fiber surface. This step of free radical polymerisation is represented by (110) in FIG. 1.

Thereafter, the PMANa-coated cotton yarns are immersed into a 39 g/L copper(II) sulphate pentahydrate solution for 0.5-1 hour, where the Cu2+ ions are immobilized onto the polymer by ion exchange. Followed by reduction in 0.1-1.0 M sodium borohydride solution, Cu2+ will be reduced to Cu particles which act as nucleation sites for the growth of Cu in the subsequent electroless deposition of Cu. This step of ion exchange and reduction is represented by (120) in FIG. 1.

The polymer-coated cotton after reduction in sodium borohydride solution is immersed in a copper electroless plating bath consisting of 12 g/L sodium hydroxide, 13 g/L copper(II) sulphate pentahydrate, 29 g/L potassium sodium tartrate, and 9.5 mL/L formaldehyde in water for 60-180 minutes. The as-synthesized Cu-coated yarns are rinsed with deionized (DI) water and blown dry. The step of performing electroless metal deposition is represented by (130) in FIG. 1 and an exemplary Cu-coated cotton yarn produced in accordance with the methods steps of this first embodiment is represented by (200) in FIG. 2.

The silane-modified cotton and PMANa-grafted cotton are able to be characterized by Fourier transform infrared spectroscopy (FTIR). As shown in FIG. 3, the presence of additional peaks located at 1602 and 1410 cm-1 represent C═C bonds in the silane molecules. Another distinctive peak located at 769 cm-1 is attributed to Si—O—Si symmetric stretching, indicating that the silane molecules are successfully cross-linked with each other on the cotton fiber surface. For the PMANa-modified cotton sample, a new peak located at 1549 cm-1 standing for carboxylate salt asymmetrical stretching vibrations confirm the PMANa grafting. Other peaks located at 1455 and 1411 cm-1 are both attributed to carboxylate salt symmetrical stretching vibrations from the PMANa.

The PMANa-grafted cotton is also able to be characterized by energy-dispersive X-ray spectroscopy (EDX). It is shown in FIG. 4 that polymerization of MANa leaves the cotton sample with a sodium element which indicates the presence of PMANa. Referring further to the FIG. 5 scanning electron microscopy (SEM) image, no obvious difference between the morphology on the surfaces of silanized cotton fiber surface and the raw cotton fiber surfaces may be visibly evident. However, after polymerization of PMANa upon the silanized cotton fiber surface, it is notable that a layer of coating had been wrapped on the cotton fiber surface. FIGS. 5D-F show that the copper metal particles are deposited relatively evenly, without any signs of cracks.

The conductivity of the copper-coated cotton yarns is able to be characterized by a two-probe electrical testing method. In this regard, linear resistance of the copper-coated yarns in the fabrication is found to be ˜1.4 Ω/cm as shown in FIG. 6A, and with superior tensile properties compared to the untreated cotton yarns, with both increase in tensile extension (+33.6%) and maximum load (+27.3%) as shown in FIG. 6B. The increase in tensile extension and maximum load is perceived to be due to the reinforcement on the strength of cotton yarns by a layer of copper.

To further test the adhesion of the copper on the cotton yarn surface and the washing durability, the copper-coated cotton yarns are first woven into a fabric first. As-synthesized copper-coated cotton yarns shown in FIG. 7A are firstly wound upon a cone as shown in FIG. 7B by use of an industrial yarn winder. Thereafter, the cone is transferred to a CCI weaving machine as shown in FIG. 7C whereby the copper-coated yarns are woven into a fabric. In the weaving setting, the copper-coated cotton yarns are configured to form the wefts of the fabric while the warps of the fabric are formed by the untreated cotton yarns as shown in the inset image of FIG. 7D which are initially mounted on the weaving machine. No problems or defects are found in the weaving process. After weaving, the fabric is cut into pieces of 5 cm×15 cm and overlocked at the four edges as shown in FIG. 7D, and subsequently, subjected to a series of washing cycles according to the testing standard AATCC Test Method 61-Test No. 2A: Colorfastness to Laundering, Home and Commercial: Accelerated (Machine Wash) (FIG. 7E) under following washing conditions:

Washing Temperature 49 ± 2° C. Volume of DI Water 150 mL No. of Steel Balls Added 50 pcs Time of Washing 45 minutes

It should be noted that according to the testing standard, 1 washing cycle is equivalent to approximately 5 commercial machine laundering cycles. In total, 6 washing cycles are conducted, which accordingly, is considered to equate to approximately 30 commercial machine laundering cycles. Changes in the electrical resistance of the washed fabrics are able to be evaluated using a four-probe method whereby the sheet resistances of the fabrics produced in accordance with this embodiment are measured to be 0.9±0.2 ohm/sq (unwashed), and 73.8±13.4 ohm/sq after the fourth wash which is equivalent to approximately 20 commercial machine laundering cycles as shown in FIG. 8.

The surface morphology of the washed copper-coated cotton yarns are able to be characterized by unraveled the washed copper-coated cotton yarns from the fabric and examined under an SEM. As shown in the SEM images of FIG. 9, it is visibly evident that the copper metal particles are retained on the surface of the cotton fibers. One perceived reason for the increase in sheet resistance is due to the loosened structure of the cotton fibers arising from repeated washing cycles.

It is also noted that during application of the standard washing cycle to the produced fabric, 50 pieces of steel balls are added into the washing canisters in seeking to simulate vigorous rubbing and stretching forces of a laundering machine. The abrasion of the steel balls on the fabric impacts substantially upon the fiber structure. As the copper-coated cotton fibers are no longer held in a tightened manner it is perceived that they lose contact with each other so as to reduce conductive pathways available for the movement of electrons. Accordingly, the sheet resistance increases upon repeated washing cycles notwithstanding, the SEM images in FIG. 9 which confirm the relatively strong adhesion of copper metal particles on the cotton fiber surface.

In alternate embodiments of the present invention, rather than coating the cotton fibers with copper particles, nickel metal particles may instead be electrolessly plated on to the textile surface by using the same approach described above. Same experimental procedures and testing may be conducted however the source of nickel that may be utilised is 120 g/L nickel(II) sulphate solution in the ion exchange procedure. Subsequently an electroless nickel plating bath is utilised consisting of 40 g/L nickel sulphate hexahydrate, 20 g/L sodium citrate, 10 g/L lactic acid, and 1 g/L dimethylamine borane (DMAB) in water for 60-180 minutes. The sheet resistance of the resulting nickel-coated cotton fabric is found to exhibit substantially similar results as that of the copper coated fiber yarns as shown in FIG. 8. Turning to FIG. 10, an exemplary nickel-coated cotton fabric is represented by (300) which exhibits a high degree of evenness of nickel metal, with bulk resistance measured as 3.2Ω.

It will be appreciated that other embodiments of the present invention may involve the use of substrates other than cotton and could be suitably applied to various textile materials such as silk, nylon and polyester. In this regard, an exemplary PAANa-assisted copper-coated yarn produced in accordance with an embodiment of the present invention is shown represented by (400) in FIG. 11A, an exemplary PAANa-assisted nickel-coated silk yarn produced in accordance with an embodiment of the present invention is shown represented by (500) in FIG. 11B, an exemplary PAANa-assisted copper-coated nylon yarn produced in accordance with an embodiment of the present invention is shown represented by (600) in FIG. 12A, and, an exemplary polyester fabric formed from PAANa-assisted copper-coated nylon yarn produced in accordance with an embodiment of the present invention is represented by (700) in FIG. 12B.

It will be appreciated from the preceding summary of the broad forms of the invention that various advantages may be conveniently provided including electrically conductive textile elements may be produced which may be suitably flexible, wearable, durable and/or washable for integration into a textile/fabric. Moreover, such high performance electrically conductive textile elements (fibers, yarns and fabrics) may be produced utilising relatively low-cost technology cost-effectively on a mass scale based upon the chemical reaction of in-situ free radical polymerization to grow negatively-charged polyelectrolytes such as PMANa or PAANa on textile substrates which may conveniently provide an improved negatively-charged polyelectrolyte layer bridging the electrolessly deposited metal and textile elements and substrates. Notably, the adhesion of conductive metal to textile substrates may be greatly improved by such surface modification of a layer of negatively-charged polyelectrolyte PMANa or PAANa, in which the electrical performance of such conductive textiles may be more reliable, robust and durable under repeated cycles of rubbing, stretching, and washing. Also, the in-situ free radical polymerization method used to prepare the negatively-charged polyelectrolyte may be performed under ambient and aqueous conditions without using any strong chemicals.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described without departing from the scope of the invention. All such variations and modification which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope of the invention as broadly hereinbefore described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps and features, referred or indicated in the specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge. 

What is claimed is:
 1. A method of producing an electrically conductive textile including the steps of: silanising a surface of the textile to provide a silanised surface; grafting a negatively-charged polyelectrolyte onto the silanised surface by in-situ free radical polymerisation; adding metal ions into the polyelectrolyte by ion exchange; reducing the metal ions to elemental metal; and coating the textile with metal particles.
 2. The method of claim 1, wherein the negatively-charged polyelectrolyte includes poly(methacrylic acid) or a salt thereof, or poly(acrylic acid) or a salt thereof.
 3. The method of claim 2, wherein the negatively-charged polyelectrolyte includes poly(methacrylic acid) sodium salt, or poly(acrylic acid) sodium salt.
 4. The method of claim 1, wherein the metal ions are copper ions.
 5. The method of claim 1, wherein coating the textile with metal particles is performed by electroless metal deposition.
 6. The method of claim 1, wherein the metal particles are nickel or copper.
 7. The method of claim 1, wherein the textile includes yarn or fibers made of cotton, nylon, silk or polyester.
 8. The method of claim 7, wherein the textile includes cotton yarn or fibers. 